1. Field of the Invention
The invention relates to a battery charger device, more particularly to a battery charger device and method for charging different types of rechargeable batteries.
2. Description of the Related Art
Devices for charging and recharging various types and sizes of storage batteries, such as nickel-cadmium (Ni-Cd) battery cells and lead-acid cells, are known in the art. There are different types of battery charger devices which are presently available to the consumers. This is due in part to the absence of a standard for regulating the voltage characteristics of the storage batteries. The fast charger is one example of a conventional battery charger device and is capable of generating a relatively large charge current in order to charge the storage battery within a relatively short period of time. The large charge current, however, can cause rapid heating of the storage battery, thereby resulting in damage to the storage battery or a reduction in the useful life of the same if the storage battery was overcharged or if the fast charger was operated in cold weather conditions.
The trickle charger is another example of a conventional battery charger device and generates a relatively small charge current, typically 10% of the maximum charge current which can be accepted by the storage battery. Such chargers do not require means for protecting the storage battery from overcharging and require relatively long charging periods. Thus, a storage battery which was charged by the trickle charger is sometimes insufficiently charged and cannot be used to drive an electrical load properly.
U.S. Pat. No. 5,055,763 discloses an electronic battery charger device which is used to charge one or more storage batteries and which comprises a circuit with terminal means that is to be connected to the storage batteries. The circuit includes a source of electric energy, controllable switching means connected respectively between the energy source and each storage battery to be charged, and a microprocessor having a control connection to each of the controllable switching means for controlling communication between the energy source and the respective storage batteries to be charged. The microprocessor includes means for sequentially controlling the switching means to supply charging current to the storage batteries one at a time in repeating periods. The circuit further includes means responsive to the voltage across the terminals of each storage battery prior to and during each charging period thereof and operatively connected to the microprocessor. The microprocessor is programmed to calculate the difference between the battery terminal voltage of each storage battery prior to and when it is being charged. The circuit also includes means for storing for each storage battery the minimum value of the voltage difference during each charging period, and means to terminate a charging operation for a storage battery when the battery terminal voltage difference being calculated exceeds the minimum stored value of the battery terminal voltage difference by a predetermined amount.
Note that in the above disclosed electronic battery charger device, the charging operation is continued until the battery terminal voltage difference exceeds the minimum stored value by a predetermined amount. This type of a charging operation is not suitable for lead-acid cells and can cause damage to the same. The battery charger device can only be used with nickelcadmium battery cells, thereby reducing the utility of the conventional battery charger device.
In the above disclosed battery charger device, trickle charging is effected when the battery voltage is less than 0.7 volts. A storage battery with such an open circuit voltage is abnormal and should not undergo a fast charging operation. Therefore, the above disclosed battery charger is not capable of performing the trickle charging operation when a normal storage battery is installed.